Modifications for the ICOM - RogerK

19-07-1998(R-7000) Modify your ICOM R7000 to scan and search fasterAuthor: Bob Parnass, AJ9SThis article describes how to increase the scan and search speeds of the ICOM R7000 receiver by 60% without noticeableperformance degradation.BackgroundThe front panel SCAN SPEED control on the R7000 receiver allows the user to adjust the speed of scan- ning and searchingoperations, as well as the rate at which the priority channel is sampled. Rotating the control counterclockwise decreases thespeed, and rota- ting it clockwise increases the speed.When the SCAN SPEED control on my R7000 (serial number 001400) was turned fully clockwise, the radio would scan amaximum of about 8 channels/second, or search about 8 increments/second. As the following table shows, the stock R7000 canscan about as fast as a Radio Shack PRO-30 or PRO-2003.TABLE 1. Maximum Scan Rates of Selected Receivers_____________________________________________________| Scanner Maximum Scan Rate|| | (channels/second)||________________________________|___________________|| Kenwood TR-2600 | 1.2 || Radio Shack PRO-30 | 8 || Radio Shack PRO-2003 | 8 || ICOM R7000 (stock) | 8 || ICOM R7000 (after modification)| 13 || Regency M400 | 13 || Bearcat 20/20 | 15 || Bearcat 300 | 15 ||________________________________|___________________|R7000 Scan CircuitsThe scan rate of the R7000 is determined, in part, by a simple clock outside the microprocessor. The front panel SCAN SPEEDrheostat and resistor R18 (and other components in the LOGIC UNIT) control the speed of this clock. The clock output isconnected to what appears to be an input port on the microprocessor. The upshot is that we can affect the scan rate withoutaffecting the other chores performed by the microprocessor.The modification consists simply of soldering a 470,000 ohm resistor across the leads of resistor R18 on the LOGIC UNIT circuitboard.How was the value of 470,000 ohms chosen? Experimenta- tion with different resistor values showed that for values both aboveand below 470,000 ohms, the R7000 scan rate decreases. Not having the R7000 Service Manual, I assume this can be explainedby the firmware within the microprocessor associated with the scan rate input port.2Adding the 470,000 ohm resistor in parallel with R18, rather than just replacing R18, has a few advantages:1. The modification is easily undone, returning the radio to stock condition.2. The LOGIC UNIT board does not have to be removed, as would be the case if R18 was unsoldered from the foil side.Making the ModificationAccessing this circuit board is not difficult, and involves the same steps used when installing the optional Remote Controller orSpeech units.Use a towel to cover your work area to avoid scratching the R7000 cabinet. Unplug the R7000 from the AC line, and turn theradio upside down. Remove the bottom cover by removing the 12 screws holding it in place. Remove the 4 screws holding whatICOM terms the "parti- tion panel". Pictures on pages 32 and 34 of the R7000 Instruction Manual show the partition panel. Afterremoving this panel, the component side of the LOGIC UNIT circuit board is accessible.Perhaps the firmware polls the scan rate input port infrequently. Another possibility is that the scanning pulses interrupt theprocessor, and the interrupt firmware is limited in its ability to process frequent interrupts.Locate R18, a 270,000 ohm 1/8 watt resistor, near con- nector J5. You may wish to remove plug P5 from J5 tem- porarily if itgets in your way. Carefully solder a 470,000 ohm resistor in parallel with R18. I used a 1/4 watt resistor as it was the smalleston hand.Reassemble the radio, connect it to AC power and antenna, and enjoy.